Lilly starts 4,500-person trial of tirzepatide and retatrutide in fatty liver disease without biopsy endpoint

Eli Lilly has begun a 4,500-participant phase 3 trial that tests tirzepatide and retatrutide against placebo in adults with metabolic dysfunction-associated steatotic liver disease, the condition also called fatty liver disease ^[1]. The study, registered as NCT07165028 under the name SYNERGY-Outcomes, is described as a master protocol of multiple agents, meaning more than one drug is evaluated under a single overarching structure ^[1].

The trial is built around hard liver outcomes rather than the liver-biopsy measures that other late-stage MASH programs have used for accelerated approval ^[1]. MASH is the progressive form of fatty liver disease. Participants are assigned to tirzepatide, retatrutide or placebo, and the study is expected to run about 224 weeks, with primary completion estimated for 2030 ^[1].

A review in the journal Med frames the field's direction as a shift "from accelerated approval to cirrhosis trial innovation," toward longer studies that measure clinical events rather than changes scored on a tissue sample ^[2].

Tirzepatide is the active ingredient in Mounjaro and Zepbound. Retatrutide is an investigational drug with no approved brand name. Neither has an approved MASH indication, so the trial is testing them as potential new uses rather than as established liver treatments ^[1].

Several details have not been disclosed. The registry record does not list the doses being tested, the specific eligibility criteria beyond adults with high-risk disease, the number or location of study sites, or whether an interim analysis is planned ^[1]. It also does not state how many participants will receive each drug. Those points have not been reported.

Why it matters for patients

The design choice is the news. MASH approvals have generally been pursued through liver biopsies, which are invasive, and biopsy scores do not always track how a patient feels or how long they live ^[2]. SYNERGY-Outcomes skips that path and asks whether the drugs reduce serious liver events ^[1].

That approach can produce answers that matter more directly to patients, but it also takes much longer. With primary completion estimated for 2030, people with fatty liver disease should not expect results from this trial in the near term ^[1]. There is no accelerated approval endpoint here, so this study cannot by itself support an early approval based on biopsy changes ^[1].

For people already taking tirzepatide, sold as Mounjaro and Zepbound, for obesity or type 2 diabetes, this trial does not change those approved uses and does not establish a liver benefit. Retatrutide is not available outside clinical trials. A trial starting does not alter current prescribing, and no dosing information for a MASH use has been reported ^[1].

People with fatty liver disease who follow research can watch for the study's eligibility criteria and site locations, which are not yet listed on the registry record ^[1]. The Med review describes the field's move toward cirrhosis outcome trials as an evolving area, and the practical effect for patients depends on results that have not been generated ^[2].

What happens next

The trial was registered with a start date of October 15, 2025 ^[1]. Primary completion is estimated for 2030, after roughly 224 weeks of study ^[1]. Enrollment status, site locations, and any plans for interim data have not been reported ^[1].